The global market for MEMS devices and nanotechnology is well established and currently is over eight billion dollars per year. Currently most microeletromechanical systems (MEMS) are constructed using modified versions of VLSI technology wherein layers of silicon nitride, silicon dioxide, and polysilicon are successively grown and patterned using photolithography. This process is inherently costly and time consuming, as there are typically as many as seven growth and lithography steps. The process is also limited by the resolution of the lithography and wet or dry etch processes to the extent that nanoscale devices are not easily achievable.
Continuous oxide films have been implanted into silicon using a SIMOX process. An O+ ion broad area beam is used for creating an unpatterned buried film under the surface of and into bulk silicon. The thickness of the buried film is determined by the concentration dose of the ion broad area beam. The bulk silicon with the buried oxygen film is then annealed to create a silicon dioxide SiO2 buried film in bulk silicon. Such buried films would normally be destroyed by conventional etching processes and are unsuitable for creating nanoscale devices, that is, ion broad area beams would not be used for creating nanoscale devices because there would be no suitable etching process for releasing the nanoscale SiO2 MEMS. The standard application is to create an electrical barrier in VLSI bulk silicon.
Typically, silicon MEMS devices are fabricated where a silicon dioxide SiO2 film is used as a sacrificial layer. Deposited or thermally grown films are used for creating layers that are patterned by photolithography and then etched away. The resolution of this process is unsuitable for making nanoscale features. Typically, MEMS devices are then released using a wet or vapor phase hydrofluoric acid to dissolve the silicon dioxide across the whole wafer at all levels. In practical terms, the wet or vapor process is limited to making polysilicon devices, as there is currently no simple means for doing the opposite. That is, there is no good method of cleanly removing the silicon while selectively leaving the silicon dioxide to form a three-dimensional structure. Therefore, the device material is restricted to polysilicon even when silicon dioxide is integral to the process. MEMS devices are typically created using conventional photolithography processes having multiple steps with limited resolution, and hence unsuitable for manufacturing of nanoscale devices.
Laser assisted chemical etching using chlorine gas has been used to etch bulk silicon. Silicon dioxide structures have been defined using standard lithographic techniques and VLSI processing. Commonly used wet etches, like EDTA or KOH, can remove silicon but are difficult to handle and the etch selectivity is highly temperature dependent. Further, wet etching of removed silicon dioxide creates stiction in the MEMS device as the surface tension of the drying liquid draws the small devices down onto the substrate. Xenon difluoride and bromine trifluoride in the vapor phase have been used to selectively remove silicon and leave silicon dioxide or nitride but the process can be very aggressive and hard to isolate and control. These release processes disadvantageously limit the ability to use the rest of the wafer for other electrical or packaging purposes and make these processes poor candidates for production environments. In the case of integrating electronics and packaging, industry is searching for improved methods, such as an electronics first method that deposits the electronics first and then uses the MEMS process to create further structures, or such as, a MEMS first method that conversely creates the MEMS first and is followed with the deposition of electronics and packaging. Neither the electronics first or the MEMS first methods are particularly suitable for high yield processes. These and other disadvantages are solved or mitigated using the invention.